ESTRO 2024 - Abstract Book

S419

Brachytherapy - Urology

ESTRO 2024

expansion. For WG salvage brachytherapy, the prescription dose was 21Gy to the entire prostate and 27Gy to the MR-defined DIL divided over two implants (3-5mm expansion) separated by 1-2 weeks. The urethra and rectal dose constraints were prioritized over dose coverage of the DIL. All patients underwent pre- and 1-2 year post-salvage mpMRI to assess response. Adjuvant androgen deprivation therapy (ADT) was not used. For the subset of patients who had recurrent/persistent disease on the post- salvage mpMRI (PIRADS≥4), we determined the patterns of recurrence and the dosimetry of the salvage HDR brachytherapy to those sites. Post-salvage biopsies were not mandated in the protocol. The dose delivered to the post-salvage site of relapse was calculated by deformable registration of the post-salvage DIL and the original treatment plan using MIMvista software.

Results:

Sixty patients (median 73 years) were treated with salvage HDR (WG n=30, FG n=30). The primary radiation for the WG cohort was 70-78Gy with conventional fractionation in 28 patients and alternate fractionation in 2 patients (35Gy/5F and 50Gy/15F). The primary radiation for the FG cohort was 70-78Gy with conventional fractionation (n=15), 19Gy/1F HDR monotherapy (n=9), 15Gy/1F HDR boost plus 37.5Gy/15F (n=2), 105Gy/1F LDR boost plus 45Gy/30F (n=1) and 145Gy/1F LDR monotherapy (n=3). For both cohorts, the overall median (range) pre-salvage HDR PSA was 4.24 (0.63-11.63). The post-salvage mpMRI (median 429 days) was performed in 27 and 28 patients who had FG and WG, respectively. It identified 16 recurrent/persistent lesions: WG: n = 9 (in-field = 6, marginal = 3, distant 0); FG: n=7 (in-field = 3, marginal = 3, distant 1). The dosimetry received by the area of post-salvage recurrent/persistent is summarized in the Table.

(n)

V27Gy (%)

V21Gy (%)

D90% (Gy)

D98% (Gy)

Focal-gland (7)

99.9 (99.7, 100)

100 (100, 100)

37.0 (32.4, 43.0)

32.8 (29.3, 36.2)

In-field (3)

43.9 (5.2, 64.3)

59.0 (22.7, 81.4)

14.0 (10.1, 18.0)

11.4 (8.3, 15.1)

Marginal (3)

Out of Field (1)

16.8

33.0

12.6

10.7

Whole-gland (9)

97.8 (92.1, 100)

100 (100, 100)

33.2 (27.7, 42.3)

29.5 (24.8, 37.7)

In-field (6)

62.3 (58.0, 68.3)

97.7 (94.1, 100)

23.3 (21.9, 25.2)

21.9 (20.0, 24.3)

Marginal (3)

Conclusion:

Our results of salvage FG and WG brachytherapy suggest that most recurrent/persistent lesions seen on the post salvage mpMRI were infield, despite optimal dosimetric coverage (V27, D90, D98). Alternate strategies for treatment intensification may be considered. Marginal recurrences were undercovered and may suggest inadequate margins.